Device for controlling a tractor-pushed agricultural implement

ABSTRACT

A device for controlling a pushable implement provided with at least one gauge wheel. The device includes a hitch system comprising two lower longitudinal arms (5, 6) with a tool-engaging member (9) at the front ends thereof, an upper engagement assembly (C) joining a third point of engagement (17) to the implement (3), at least one lifting jack (12, 13), and a distribution unit (21) for controlling the raising and lowering of the longitudinal arms (5, 6). A controller (28) operates the distribution unit in response to a degree of slippage measured by a unit (M). The upper engagement assembly (C) includes at least one third-point jack (18; 18a, 18b) connected to a second fluid distribution unit (30, 30&#39;) controlled by said controller (28) so that when the longitudinal arms (5, 6) are raised, the second distribution unit (30, 30&#39;) switches to a position in which part of the load is shifted onto the tractor as the lower longitudinal arms are raised.

This application is the national phase of international applicationPCT/FR95/00996, filed Jul. 25, 1995 which designated the U.S.

The invention relates to a device for controlling an agriculturalimplement equipped with at least one gage wheel and intended to bepushed by a tractor, the device being of the sort comprising a hitch andlift system intended to be mounted at the front of the tractor in orderto fasten the implement, this system including:

two lower longitudinal arms, the rear parts of which include means ofarticulation to the structural part of the tractor, and the front endsof which are equipped with a means of attaching the implement in orderto constitute two bottom attachment points,

an upper attachment member for linking a third attachment point of thetractor to the implement, the latter being equipped, at its rear part,with three attachment means which are the conjugate of those of thehitch system,

at least one lifting ram and distribution means for controlling theraising or lowering of the longitudinal arms;

and a controller which commands these distribution means in response toinformation regarding the slippage of the tractor originating fromslippage-measuring means provided on the tractor,

the assembly being arranged so as to command a raising of the lower armsand a reduction in the working depth of the implement when the amount ofslippage of the tractor becomes greater than a given reference value.

A device of this sort is known from FR-A-2,649,810 and plays a part inimproving the working conditions of the tractor. However, although thereduction in depth by reducing the effort required is accompanied by areduction in slippage, there is no improvement in the traction. One ofthe objects of the invention is for the reduction in working depth ofthe implement to be accompanied by a transfer to the tractor of the loadnormally supported by the gage wheels of the implement.

Another cause of loss of traction is explained hereafter.

Pushed implements which work in the ground are equipped with gage wheelsespecially to allow them to follow the lie of the land in allconditions.

In order to avoid mechanical stresses which are detrimental to theoperation of the tractor/implement combination, it is appropriate, whenworking the ground, for the hydraulic hitch and lift system to act in afloating mode so as to allow the longitudinal and possibly transverselie of the land to be followed, or for the front lift to be equippedwith means allowing the implement to pivot longitudinally (pivotingabout an axis substantially parallel to the axes of the wheels of thetractor) and possibly laterally (pivoting about an axis parallel to thelongitudinal axis of the tractor), with respect to the lift system.

Using the hydraulic lift system in floating mode does not allow theimplement to be supported during work, and this implement is thereforesupported essentially by the gage wheel or wheels. This results in aloss of traction at the tractor and in difficulty in driving the latter.The implement is tricky to adjust.

The use of an upper attachment member formed by a sliding link system,combined with holding the lower arms in position, makes it possible tobear some of the weight of the implement and simplify adjustment.However, a substantial amount of the weight of the implement is stillsupported by the gage wheels. Here too this results in a loss oftraction at the tractor.

In order to improve the traction of tractors, there is known, fromFR-A-2,512,319, a device in which the upper attachment member comprisesat least one ram, while a system of load sensors is provided on the gagewheel or wheels so as, by means of an electro-hydraulic unit, to commandfeed to the top link ram in order to remove some of the weight borne bythe gage wheels and transfer it to the tractor to improve its traction.

A significant drawback in such a device is that it requires gage wheelsequipped with sensors for each implement. This results in an appreciablepurchase on-cost, and an additional maintenance burden because thesensors, which are highly stressed, are situated in regions which areexposed to attack. In addition, it is necessary to provide on theimplement passage for the bundles of electrical cables which areintended to connect the sensors to the electro-hydraulic unit, and forthese bundles to be connected up to the tractor. These operations may bethe source of errors and may lengthen the time taken to couple theimplement to the tractor. Furthermore, the connections may be thesources of breakdowns.

Another object of the invention is to improve the traction of thetractor without having to use sensors on the gage wheels, or bundles ofelectric cables providing connection between these sensors and thetractor.

Furthermore, it is desirable for the control device, while optimallytransferring load to improve the traction of the tractor automatically,and without resorting to sensors on gage wheels, to allow thelongitudinal and possibly the transverse lie of the land to be followed.

According to the invention, a device for controlling an agriculturalimplement equipped with at least one gage wheel and intended to bepushed by a tractor, of the sort defined previously, is characterized inthat, in a way known per se, the upper attachment member comprises atleast one third point ram, connected to second fluid-distribution meanscapable of adopting a first position in which the variations in lengthof the assembly of the rod and of the cylinder of the third point ramare free, and a second position for which the third point ram plays apart in transferring load from the gage wheel to the tractor, and inthat these second distribution means are operated by the abovementionedcontroller in such a way that when raising of the longitudinal lowerarms takes place, the second distribution means switch into their secondposition in order to transfer some of the load on the gage wheel orwheels of the implement toward the tractor at the same time as a commandto reduce the working depth of the implement.

The geometric configuration of the hitch system is preferably such that,as required in the standards, when raising of the lower arms iscommanded, the third point ram is made to extend; advantageously,according to the invention, the second distribution means, in theirsecond position, block the liquid in that chamber of the ram which iscompressed upon lengthening and therefore block the overall length ofthe third point ram in such a way that the raising of the lower arms isthen accompanied by a lifting-up of the front part of the implement anda lightening of the gage wheel or wheels with automatic load transfer tothe tractor.

Advantageously, the third point ram is of the double-acting type andeach of the chambers situated on either side of the piston is connectedto the second fluid-distribution means.

As a preference, the second distribution means are operated electricallyand the layout is designed so that when the control device iselectrically powered, the distribution means switch into their firstposition corresponding to a floating mode, whereas in the event of theelectrical supply being cut off, the second distribution means switchinto the second position, blocking the length of the third point ram.

Advantageously, the second distribution means, in their first position,are capable of forcing liquid under a relatively low pressure,particularly one lower than 20 bar, into the rod-side chamber of theram, in order to avoid the phenomenon of cavitation, while the otherchamber is connected to tank (reservoir of liquid at atmosphericpressure).

In cases where just one third point ram is provided, for example incases where the implement is equipped with just one gage wheel, thesecond distribution means operating this third point ram advantageouslyinclude a third position which allows the distribution of the fluid tobe reversed by comparison with the first position and a lengthening ofthe ram to be commanded, the switching of the second distribution meansinto this third position being commanded with the aid of an externalcontact button, particularly during implement-attachment operations.

An intermediate frame, especially one in the shape of an inverted U, asshown in FR-A-2,649,580 may be provided between the points of attachmentof the hitch system and the implement. In this event, the control deviceincludes two third point rams forming between them an angle the vertexof which corresponds to the third point of attachment to the structuralpart of the tractor, and the ends of which correspond to two lateralattachment points provided on the upper part of the frame, symmetricallywith respect to the third point of attachment of the implement, situatedin the middle of the upper part of the frame.

The second distribution means, for a system with two double-acting thirdpoint rams, are arranged so that in their first position they form abridge placing the two ram-side chambers of the two third point rams incommunication, while the two other chambers of the rams are connected totank.

Advantageously, the two lower longitudinal arms of the hitch system arecapable of relative motion one with respect to the other and may adoptdifferent inclinations one with respect to the other.

When the hitch system comprises an intermediate frame, the controldevice preferably comprises third two-position distribution meansarranged on a pipe connected in parallel to the two third point ramchambers opposite the rod; these third distribution means in a firstposition (normal operation) link the chambers opposite the rod to thelow-pressure liquid reservoir, while in a second position, commandedfrom the outside, these third distribution means ensure that a liquidunder the same pressure as the liquid let into the rod-side chambers islet into the chambers opposite the rod so that through a differentialeffect which is due to the cross-sectional area of the rod, there is alengthening of the third point rams, especially with a view to making iteasier to attach the third top point of the implement after the twolower points have been attached.

The intermediate frame may include, at the top in the middle, tworearwardly projecting flanges equipped, at their rear end, with a holeor the like for attaching a third point bar, particularly anadjustable-length bar.

The points of attachment of the hitch system, particularly the thirdpoint bar, are arranged to allow automatic coupling, means indicatinglocking advantageously being provided.

The invention consists in a certain number of other arrangements apartfrom the arrangements revealed hereinabove, and these will be dealt withmore fully hereafter with regard to embodiments described with referenceto the drawings appended hereto, but which are not in any way limiting.

FIG. 1 of these drawings is a diagrammatic view in perspective of anagricultural implement hitched to the front of a tractor.

FIG. 2 is a diagram of the control device according to the invention.

FIG. 3 is a diagrammatic elevation view illustrating the operation ofthe device according to the invention.

FIG. 4 is a diagrammatic perspective view of a hitch device with theintermediate frame.

FIG. 5 is a diagrammatic front-on view of the device of FIG. 4 to whichan implement is hitched.

FIG. 6 is a diagram of the control device according to the inventionwith hitch system according to FIGS. 4 and 5.

FIG. 7 is a side view of an intermediate frame with a top third pointaccording to the invention.

FIG. 8 is a rear view of the frame of FIG. 7.

Finally, FIGS. 9 and 10 diagrammatically illustrate an automaticcoupling top bar.

Referring to the drawings, especially to FIGS. 1 and 3, it is possibleto see a tractor 1 equipped at the front with a hitch and lift system 2to which is attached an implement 3 intended to be pushed by thetractor 1. The implement 3 represented diagrammatically in FIG. 1 is awide implement, for example of the wide chisel plow type and includes,on each side, at its front end, a gage wheel 4. In the case of anarrower implement, for example in the case of a plow, just one gagewheel will be provided at the front of the implement. Of course, thetractor 1 is generally equipped at the rear with one or more otherimplements which have not been represented in the drawings.

The hitch and lift system 2 includes two lower longitudinal arms 5, 6,the rear parts of which include means 7 of articulation to thestructural part 8 of the tractor and the front ends of which areequipped with conventional attachment means 9, such as an attachmentbracket. These two attachment means 9 constitute two bottom attachmentpoints for the implement 3 which is equipped in the conventional way atits rear end with three attachment points, namely two lateral bottompoints 10 and a middle top attachment point 11.

A lift ram 12, 13 is associated with each arm 5, 6 to control theraising or the lowering of this arm. That end of the cylinder of eachram 12, 13 which is furthest from the piston rod is articulated to atransverse spindle 14 borne by the tractor 1. The rod 15, 16 of thepiston of each of the rams is connected by a transverse articulation tothe associated longitudinal arm 5, 6. As an alternative, each ram couldbe reversed and fulfil the same functions.

In the example under consideration, the arms 5 and 6 are capable of arelative motion one with respect to the other, giving rise to pivotingabout an imaginary longitudinal axis without a change in height. In analternative form, the arms 5 and 6 could be connected together rigidly,in which case just one lift ram could be provided.

The hitch system 2 comprises an upper attachment member C connected to athird point 17 of attachment of the tractor situated above andequidistant from the two bottom attachment points 7. The top attachmentmember C consists, in the embodiment of FIG. 1, of a third point ram 18.That end of the cylinder of the ram 18 which is furthest from the pistonrod 19 is connected by an articulation to the attachment point 17 of thetractor. The piston rod 19 at its outer end carries a means 20 ofattachment for the conjugate top attachment point 11 of the implement.

Distribution means, preferably consisting of an electro-distributor 21(FIG. 2) are provided for controlling the inlet or discharge of liquidunder pressure into or out of the rams 12, 13 and thus controlling theraising or the lowering of the longitudinal arms 5, 6.

The rams 12, 13 are single-acting, but could be double-acting. The lowerchambers of the cylinders, these chambers being situated on the rodside, are connected up in parallel by a liquid pipe 22 to one port ofthe distributor 21. The pipe 22 which is T-shaped in order to provideparallel feed may comprise flexible portions. The distributor 21, whenthe slide valve is in the neutral position, isolates the pipe 22 fromthe pressure source P and from the tank 23 or reservoir of liquid whichis not under pressure. The fact that the chambers of the rams 12, 13 arelinked in parallel allows liquid to be transferred from one ram to theother and allows the abovementioned symmetric relative motion inopposite directions of the arms 5, 6 one with respect to the other, withthe implement 3 pivoting about an imaginary longitudinal axis withoutchange in height.

The distributor 21 includes two electromagnet coils 24, 25. When voltageis applied to the coil 24, the slide valve of the distributor 21switches into a position (right-hand box) in which the liquid underpressure is sent into the lower chamber of the ram 12 or 13, whichcauses the rod 15, 16 to retract and the associated arm 5, 6 to beraised. When voltage is applied to the coil 25, the slide valve of thedistributor 21 switches into a position (left-hand box) in which thepipe 22 is connected to the tank 23. The liquid can therefore flow outof the lower chamber of the ram 12, 13, which pushes out the rods 15, 16and causes the arms 5, 6 to be lowered under the effect of the load theyare bearing.

Means M are provided for measuring the slippage of the tractor relativeto the ground. These means M comprise, for example, a radar 26 fixed tothe structural part of the tractor, pointing toward the ground, andcapable of providing the actual speed of the tractor 1 relative to theground as explained in FR-A-2,649,810. A sensor 27 is furthermoreassociated with a driving wheel of the tractor, to count the number ofwheel revolutions per unit time and determine, from the perimeter of thewheel, the theoretical speed that the tractor should have in the absenceof slippage. The information provided by the radar 26 and the sensor 27is sent to inputs of an electronic calculation circuit 28 comprising,for example, a microprocessor, capable of determining the amount ofslippage. The electronic calculation unit 28 compares the calculatedamount of slippage with a reference value. If the calculated amount ofslippage becomes higher than the reference value, then the unit 28 onone of its outputs connected to the coil 24 by an electric connection 29provides a command voltage to make the slide valve of the distributor 21switch into the position which allows liquid under pressure to be letinto the lower chamber of the rams 12, 13. This results in raising ofthe arms 5, 6 and in lifting-up of the implement 3. The working depth ofthis implement 3 reduces, which causes a reduction in the pushing forceto be exerted by the tractor 1 and tends to reduce the slippage.

The control device D of the invention comprises (in addition to thehitch system, the distribution means 21 and the controller 28 whichcommands as a function of the slippage of the tractor) secondliquid-distribution means 30. The third point ram 18 is double-actingand its two chambers are connected by respective pipelines 31, 32 to twoports of the second distribution means 30. These means 30 consist of anelectro-distributor 33 the slide valve of which is commanded by twoelectromagnetic coils 34, 35 provided at each end of the distributor.When voltage is applied to neither of the coils 34, 35, the distributor33 is in its second position, or neutral position, illustrated in FIG.2, for which the two pipelines 31, 32 are closed. In these conditions,the liquid lying in the two chambers of the ram 18 which are situated oneither side of the piston is trapped; the piston of the ram 18 and therod 19 connected to this piston cannot move because the liquid isconfined to a closed volume; the overall length of the ram 18 is blockedat a constant value. The distance between the point 17 of articulationof the tractor and the attachment means 20 which receives the topattachment point of the implement 11 is also constant.

It should be noted that the distance between the articulations 7 and 17on the tractor side is less than the distance between the articulations10 and 11 on the implement side, which means that the raising of thearms 5, 6 and of the top attachment point 11 makes the ram 18 extend.

When voltage is applied to the coil 34, the slide valve of thedistributor 33 moves to the left in FIG. 2, to adopt its first position,which means that the pipeline 32 which opens into that chamber of theram 18 which is on the rod side, finds itself connected to a pipeline 36able to supply liquid under a relatively low force-feed pressure comingfrom an auxiliary source other than the pump supplying the pressure P.An adjustable restriction 36a may be provided on the pipeline 36. Withthe slide valve in this first position, the pipeline 31 is connected toa pipeline 37 leading to the tank. By way of nonlimiting indication, theforce-feed pressure of the liquid in the pipeline 36 does not exceed 20bar, whereas the pressure P may be as high as about 200 bar.

The liquid under force-feed pressure supplied by the pipeline 36 makesit possible to avoid a phenomenon of cavitation in the rod side chamberof the ram 18, but has no appreciable influence on the motion of thepiston when the implement 3 is hitched, because this force-feed pressureis too low by comparison with the pressures developed by the reactionsof the implement on the hitch system. The other pipeline 31 is connectedto the tank 23 when the coil 34 is energized. It may thus be seen thatthe motion of the rod 19 of the ram 18 is free, when the coil 34 isenergized, because the liquid contained in each of the chambers can bedischarged freely in response to the motion of the rod 19 due to thereactions of the implement 3.

The second distribution means 30 are commanded by the controller whichconsists of the electronic unit 28 combined with the sensor 27 and theradar 26 in such a way that when raising of the longitudinal arms 5, 6takes place, the distributor 33 switches into the second position(neutral position) represented in FIG. 2, blocking the length of the ram18.

Advantageously, the output of the electronic unit 28 used to command thecoil 24 of the electro-distributor 21 (in order to raise the arms 5, 6)is used to command the other coil 34. An invertor circuit 38 is providedbetween the output of the circuit 28, which output is connected to thecoil 25, and the coil 34; in these conditions, when no command voltageis supplied to the coil 24, the reverse circuit 38 gives on its output avoltage which is applied to the coil 34; the distributor 33 is thereforeheld in its first position (free variation in length of the ram 18) whenthere is no command to raise the arms 5, 6.

By contrast, when there is voltage on the coil 24, causing the slidevalve 21 to move into the position which raises the arms 5, 6, thevoltage on the coil 34 disappears and the slide valve 33 switches intoits second position, illustrated in FIG. 2, causing the length of theram 18 to be blocked.

When voltage is applied to the coil 35, this coil makes the slide valve33 switch into a third position for which the liquid under force-feedpressure coming from the pipeline 36 passes into the pipeline 31 openinginto that chamber of the ram 18 which is opposite the rod 19, whereasthe pipeline 32 is connected to tank. Voltage may be applied to thewinding 35 using an external command involving a contact 39.

The application of power to the coil 35 is commanded, as explainedlater, with a view to facilitating the attachment of the implement 3,while the hitch system is not subjected to loadings from the implement3. The force-feed pressure coming from the pipeline 36 is thensufficient, when let into that chamber of the ram 18 which is oppositethe rod 19, to push this rod 19 out and lengthen the ram.

Of course, the electric commands for powering the various coils 24, 25and 34, 35 are designed to be such that they prevent voltage from beingapplied to two opposed coils simultaneously.

This being the case, the control device D operates as follows.

Referring to FIG. 3, it is possible to see, in thick solid line, therelative positions of the tractor, of the implement, and of the hitchsystem (represented diagrammatically) when the amount by which thetractor 1 slips is below a reference value.

As explained earlier, the distributor 33 (FIG. 2) is in its firstposition, the coil 34 being energized, in which position the variationsin length of the third point ram 18 are free. The implement 3 will beable to follow the land, in the longitudinal sense, by rotating about ahorizontal transverse geometric axis passing through the bottomattachment points 10 (see FIG. 1).

If the amount of slippage exceeds the reference value, the electronicunit 28 acts on the distributor 21 to command the retraction of the rods15, 16 of the rams 12 and 13 and the raising of the arms 5, 6.

In the absence of the second distribution means 30 in accordance withthe invention, the implement would adopt the position represented infine solid line in FIG. 3, for which the bottom attachment points 10 areraised while the top attachment point 11 would tilt forward, movingupward, which would cause a lengthening of the ram 18. The load to whichthe gage wheel 4 is subjected would remain substantially the same aswould the load borne by the tractor. There is therefore no improvementin the traction, even if there is a reduction in the slippage combinedwith the reduction in pushing effort required.

According to the invention, thanks to the combination of all of thecontrol means with the second distribution means 30, when thedistributor 21 switches into the position commanding the raising of thearms 5, 6, the second distribution means 30 switch into their secondposition illustrated in FIG. 2, by cutting off the excitation of thecoil 34. The liquid is therefore trapped in the chambers of the ram 18,the length of which is blocked at a constant value. In these conditions,as illustrated in broken line in FIG. 3, when the arms 5 and 6 areraised, the ram 18 pivots about the spindle 17, at constant length, andthe front part of the implement 3 is therefore lifted up and the gagewheel or wheels 4 is or are lightened with load being transferredautomatically onto the tractor, the traction of which is improved.

The increase in load as the implement 3 is raised may squash the tiresof the tractor but does not lead to an increase in the working depth ofthe implement. The control device acts automatically by continualincrementation in order permanently to match the load transfer to thetraction conditions required, and the length of the ram 18 to theimplement following the lie of the land.

The control device has the advantage of being completely independent ofthe implement and of requiring no adjustment, thus avoiding the presenceof sensors on the gage wheel and of electric connecting wires.

Referring to FIG. 4, it is possible to see a hitch system involving anintermediate frame 40 in the shape of an inverted U as shown byFR-A-2,649,580. The frame 40 is arranged between the attachment pointsof the hitch system and the three attachment points of the implement.

The control device D includes two third point rams 18a, 18b formingbetween them an angle the vertex of which corresponds to the third point17 of attachment on the tractor. The rams 18a, 18b are of thedouble-acting type as is the ram 18. The ends of the rods 19a, 19bcorrespond to two lateral attachment points 41a, 41b provided on theupper part of the frame 40 symmetrically with respect to the thirdattachment point 20 situated in the middle of the top of the frame,toward the front. The frame 40 furthermore includes two lateral bottomattachment points 42, 43 (produced in the conventional way usingattachment brackets with blocking device) for the bottom attachmentpoints of the implement. At the bottom at the rear and on each side, theframe 40 includes attachment points 10a borne by the ends of the arms 5,6.

As visible in the diagram of FIG. 6, the second distribution means 30'for feeding the two third point rams 18a, 18b, comprise anelectro-distributor 33' equipped with an electric command coil 34' andwith a return spring 44 for return to the neutral position or secondposition for which the two pipelines 32a, 32b leading from the chamberson the rod side of the rams 18a, 18b are closed, which corresponds tothe length of the rams 19a, 19b being blocked.

The two ports of the distributor 30' which are opposite the portsconnected up to the pipelines 32a, 32b are connected to one another by abridge 45, and are connected by the pipeline 36' to a source of liquidunder force-feed pressure, generally below 20 bar. An adjustablerestriction 36'a may be provided on the pipeline 36'.

When voltage is applied to the coil 34', the slide valve 33' switchesinto its first position for which the two pipelines 32a, 32b areconnected to the bridge 45 and to the pipeline 36'.

The control device D' furthermore comprises third distribution means 46arranged on the pipe 31b connected up to that chamber of the ram 18bwhich is opposite the rod 19b. A pipeline 47 connects up in parallel thetwo chambers opposite the rods of the rams 18a, 18b; these two chambersare therefore fed in parallel by the pipeline 31b. The thirddistribution means 46 comprise a slide valve 48 which can adopt twopositions under the action of an electric coil 49 and of a spring 50acting in opposition to the coil, respectively.

The distributor 46 includes two ports on the opposite side to thepipeline 31b, one of the ports being connected by a pipeline 51 to thebridge 45 and therefore to the pipeline 36'. The other port is connectedby a pipeline 52 to tank. In a first position, or neutral position,represented in FIG. 6 and corresponding to the coil 49 not beingenergized, the slide valve 48 establishes a link between the pipeline31b and the pipeline 52, while the pipeline 51 is closed. In theseconditions, when the coil 34' is energized, the lengths of the rams 18a,18b can vary freely. The motions of extension or of retraction of therams 18a, 18b are possible as a function of the lie of the land overwhich the gage wheel or wheels of the implement is/are running.Fluctuations are taken into account by the bridge 45, with a volume ofliquid being transferred from one chamber of one ram into the other. Thegage wheels 14 sic! ensure that the implement is stable.

As explained earlier, when the control device commands a raising of thearms 5, 6, the second distribution means, the coil 34' of which is nolonger energized, is commanded at the same time. The slide valve 33'switches into the neutral position and closes the rod side chambers ofthe two rams 18a, 18b, the lengths of which are blocked.

The geometry of the assembly is such that raising the arms 5, 6 (and theimplement) leads to a demand to lengthen the rams 18a, 18b; since theserams are blocked, the front part of the implement is lifted up and thegage wheels are lightened with load being transferred to the tractor andthe traction being improved (see FIG. 3).

The coil 49 of the third distribution means 46 may be commanded from theoutside using a contact 53 which allows this coil to be electricallypowered. When a command is given, from the outside, by an operator, toenergize the coil 49, the slide valve 48 switches into its secondposition for which the pipeline 51 finds itself connected to thepipeline 31b and to those chambers of the rams 18a, 18b which areopposite the rods. As long as the rods 19a, 19b do not encounterappreciable resistance, for example if the implement is not attached,then the force-feed pressure supplied by the pipeline 52 will besufficient to cause the lengthening of the rams 19a, 19b the rod sidechambers of which are connected by the pipelines 32a, 32b to thepipeline 36'. Through a differential effect owing to the larger workingcross-sectional area of the chambers opposite the rods 19a, 19b, therewill indeed be a lengthening of the rams 18a, 18b when the coil 34 isenergized.

Referring to FIGS. 7 and 8, it is possible to see an alternative form40' of the intermediate frame which includes, at the top in the middle,two flanges or cheeks 54, 55 projecting backward (instead of includingthe top attachment point 20') and delimiting an empty space betweenthem. The flanges 54, 55 are equipped, toward their rear end, with ahole 56 for the passage of an attachment spindle of a third point bar57, the length of which is preferably adjustable. This bar 57 cantherefore pivot, between the flanges 54, 55, about a substantiallyhorizontal axis passing through the holes 56. The front end of the bar57 is equipped with an attachment means 58 for the top attachment point11 of the implement. The bar 57 may be held with a possibility to rotateabout the axis 56 sic! by flexible links such as a chain and a springwhich are attached at points on the frame 40' which are situated higherup than the axis 56 sic!.

When a voltage is applied to the control device D or D', for examplewhen the electric commands of the device are initialized, as alreadyexplained, the second distribution means 30 or 30' adopt the firstposition for which the rod side chambers of the rams 18, or 18a, 18b,are connected to the force-feed pressure arriving via 36 or 36'. Thispressure is sufficient to keep the rams under hydraulic tension when theload of the implement is not applied to the ends of the rods 19, 19a,19b.

This may result in a certain amount of difficulty in coupling theimplement 3, especially to the top point 11.

The intermediate frame 40 or 40' aims to make this implement-couplingoperation easier, but because this frame is situated in front of thetractor, the operator may not be able to see the entire mechanism, whichmeans that the coupling difficulty remains.

The third position of the distributor 30 or the second position of thethird distribution means 46 of FIG. 6 allow this drawback to beovercome.

In order to couple the implement 3 to the front of the tractor, from thedriver's position, it is necessary merely to proceed as follows.

It is assumed that the implement 3 is lying on ground which is notnecessarily horizontal, and that the rear bottom attachment points 10are not at the same height; for example, the bottom attachment point 10situated to the left, when viewed from the driver's seat of the tractor,is the lower.

On being brought into operation, the rod side chambers of the rams 18a,18b are connected to the pipeline 36' through which liquid arrives atforce-feed pressure. As the implement 3 is not attached to the hitchsystem, the rods 19a, 19b retract into the rams 18a, 18b and the frame40 is made to pivot backward about an imaginary transverse geometricaxis passing through the bottom attachment points 10a (FIG. 4).

The operator brings the tractor up close to the rear attachment pointsof the implement, having lowered the arms 5, 6 enough for the hooks 42,43 of the frame 40 to lie below the lowermost attachment point 10 of theimplement.

When the hooks 42, 43 lie under the attachment points 10 of theimplement, the operator commands the raising of the arms 5, 6.Attachment will occur first of all between the hook 42 and the lowerleft-hand attachment point 10 of the implement, which is the lower one.

Because the arms 5, 6 are independent and because the rams 12, 13 arefed in parallel from the distributor 21, the pressure P will not riseenough (to raise the arm 5 already attached) until the ram 13,commanding the arm 6, is also subjected to a load after attachment ofthe hook 43.

Thus, after the hook 42 becomes hitched, this hook will remainstationary while the hook 43 will continue to rise until the bottomattachment point 10 situated to the right (viewed from the tractor)engages in the hook 43. At this instant, the two lower points 10 areengaged in the hooks 42, 43 and the frame 40 has turned about animaginary longitudinal axis to adopt a transverse inclination similar tothat of the implement. This inclination is made possible by thelengthwise freedom of the third point rams 18a, 18b.

The backward pivoting of the upper part of the frame 40 discussedearlier makes it possible to be sure that the two lower points 42, 43stay the furthest forward, which makes them easier to couple to thebottom points 10 of the implement, without there being any interferenceat the top attachment point.

Locking detectors may be installed on the intermediate frame, forexample in the form of indicator lights, to inform the operator thatattachment of the lower points is complete.

When the lower points 42, 43 have been coupled to the implement, the topattachment point 20' will be facing, but behind, the top attachmentpoint 11 of the implement.

In order to attach the top point 20', all the operator will need to dowill be to act on the external command contact 53 to bring about thelengthening of the rams 18a, 18b, by sending the force-feed pressureinto those chambers of these rams which are opposite the rod. The frame40 therefore tilts forward about the imaginary transverse axis passingthrough the points 10a until the top point 11 of the implement isattached to the point 20' of the frame 40.

The external command 53 for the distributor 46 is designed in such a waythat the motion of the rams 18a, 18b is halted as soon as the contact 53is released.

A second circuit-breaking contact, operating in the same conditions asthe contact 53, may be provided to command the shortening of the rams18a, 18b so as to have complete freedom of command at the time theimplement is attached.

Of course, said external commands may be duplicated in the cab so thatthe complete attachment operation may be performed without having toleave the driving seat.

As already indicated with regard to FIGS. 7 and 8, a U-shaped frame 40'according to the invention is advantageously equipped with two cheeks54, 55 projecting backward for linking the top middle point of the frameto the implement, in place of a conventional stationary hook.

This special arrangement of the middle top part of the frame 40' ispermitted by the link to the tractor being produced by means of the twotop rams 18a, 18b arranged to form a triangle. The adjustable top bar 57of the frame 40' can be adjusted to suit the varying geometries ofimplements, without affecting the geometry of the lift.

This arrangement allows the intermediate frame 40' to become universal,thus permitting the coupling of implements having beam heights definedaccording to the standards which differ depending on the country, forexample ISO, SAE etc. standard, or depending on constraints specific tothe implement.

As explained earlier, the device allows complete automatic coupling ofthe implement, by proceeding in the stepwise manner already described.

The centering of the intermediate frame, when connecting the lowerpoints of the implement, guarantees an alignment which makes it possibleto envisage, at the top, the automatic coupling of hydraulic andelectrical functions which may be provided for the automatic-control ofthe implement.

The fact that the implement can be coupled without it being necessary tolift it up completely is an additional advantage as regards safety,because it eliminates the risk of a dropping which may arise during theattachment phase with a conventional intermediate frame when couplinghas not been carried out correctly.

In order to carry out this automatic coupling using a frame 40' as shownin FIGS. 7 and 8, the top link bar 57 is advantageously equipped with anautomatic hook 60 as illustrated in FIGS. 9 and 10 so that the couplingof the three points of the implement may be completed automatically.

Referring to FIG. 9, it is possible to see a top link bar 57' equippedwith the automatic hook 60. The bar 57' preferably has an adjustablelength; it is equipped at its end furthest from the hook with a balljoint 61 which can be mounted between the cheeks 54, 55 (FIGS. 7 and 8)with the aid of a spindle passing through the holes 56.

The hook 60 is articulated about a spindle 62 provided at the front endof the bar 57', arranged in the form of a fork. This fork has twobranches separated by a gap in which the hook 60 is mounted so that itcan rotate, the concavity of the hook pointing downward. At its rearpart pointing toward the ball joint 61, this hook 60 includes a lowerextension 63 below the bar 57'. A pin 64 is fixed to this extension 63for attaching to one end of a tension spring 65, the other end of whichis attached to a pin 66 borne by a sort of bracket 67 secured to the bar57' and projecting upward above the hook 60. The pins 64 and 66 arearranged in such a way that when the hook is in the open position, asillustrated in FIG. 9, the geometric axis of the spring 65 lies ahead ofthe spindle 62 about which the hook 60 rotates. The return spring forceexerted by the spring 65 therefore tends to keep the hook 60 open.

When the hooks are in the closed position, as illustrated in FIG. 10,the geometric axis of the spring 65 has moved behind the rotationspindle 62 which means that the action of the spring 65 tends to closethe hook 60. During pivoting from the open position to the closedposition or vice versa, the geometric axis of the spring 65 thereforeswitches from one side of the spindle 62 to the other.

A position detector 68, for example with an electric contact, may befixed to the arm 57' sic! in such a way that it is actuated by the lowerend of the extension 63 when the hook 60 is in the locked positionillustrated in FIG. 10. The locking information may be transmittedthrough an electric wire to the control panel of the tractor.

A safety lock 69, consisting for example of a pawl articulated to thebar 57' at a point situated behind the hook 60 may be provided. Thislock 69 situated at the top of the bar 57' can be braced against anabutment region 70 on the hook 60 in the closed position, under theaction of a return spring.

An unlocking handle 71 articulated to the hook is provided so as toallow an operator to lift up the lock 69 and unlock the hook 60.

At its front lower end, the bar 57' is equipped with a downwardlyinclined guide piece 72.

When the hook 60 is in the open position, it projects via a cam-shapedboss 73 over the surface of the guide 72. This boss 73 has a shape whichis suitable to cause the hook 60 to pivot toward its closed positionwhen the boss 73 comes into contact with the top attachment point 11 ofthe implement, this generally consisting of a cylindrical spindle.

The way in which the automatic hook operates is immediately obvious fromthe previous explanations.

As already explained, the bar 57' retains a certain possibility forexcursion about the spindle on which the ball joint 61 is mounted. Whenthe operator, after having attached the bottom points of the frame 40',commands the forward pivoting of this frame 40', by lengthening the rams18a, 18b, the hook 60, in the open position, is moved closer to the topattachment point 11 of the implement.

This attachment point 11, guided by the piece 72, will come into contactwith the boss 73 and cause the hook 60 to close when the frame 40' hasfinished pivoting forward.

I claim:
 1. A device for controlling an agricultural implement having atleast one gage wheel and a frame adapted to be pushed by a tractor,comprisinga hitch having three attachment points and lifting devicesmountable on the front of a tractor including: two arms each having oneend provided with articulation means for attachment to the tractor andopposite ends each provided with means for attachment to the implementto thereby define two attachment points; an attachment member locatedvertically above said two arms and defining a third attachment pointbetween the tractor and the implement, said implement including a rearpart having three attachment means for cooperating respectively withsaid three attachment points of the hitch, at least one lifting ram anda first fluid distribution means for controlling the raising andlowering of said two arms, a controller for controlling saiddistribution means in response to slippage of the tractor where thetractor is provided with slippage measuring means, said controllerhaving a reference value so that, when the slippage exceeds thereference value, said controller will effect raising of said two arms toreduce the working depth of the implement, said attachment memberincluding at least a third point ram connected to a second fluiddistribution means, said third point ram having a piston having on oneside a rod and cylinder with said piston and rod being movable relativeto said cylinder, said second fluid distribution means having a firstposition in which said piston, rod and cylinder are freely movable and asecond position in which said third point ram is locked to transfer aload from the gage wheel to the tractor, said second fluid distributionmeans being controlled by said controller so that, when said two armsare raised, said second fluid distribution means moves from said firstto said second position to transfer at least some of the load on thegage wheel to the tractor, said third point ram being connected betweenthe tractor and said implement so that, when said two arms are raised,said third point ram is extended, said second fluid distribution means,when in said second position, blocks flow of fluid in said third pointram which becomes compressed when said third point ram is extendedwhereby the raising of said two arms effects lifting of the front of theimplement to effect said transfer of the load on said gage wheel to thetractor.
 2. Control device according to claim 1 wherein the seconddistribution means (30, 30') is operated electrically and the layout isdesigned so that when the control device is electrically powered, thedistribution means (30, 30') switch into their first positioncorresponding to a floating mode, whereas in the event of the electricalsupply being cut off, the second distribution means switch into thesecond position, blocking the length of the third point ram (18; 18a,18b).
 3. The device as claimed in claim 1 wherein said one lifting ramis controlled by said first fluid distribution means.
 4. The device asclaimed in claims 1 or 3 wherein said third point ram has two chamberslocated on either side of said piston, each chamber being connected tosaid second fluid distribution means.
 5. The device as claimed in claim1 wherein said piston of said third point ram has a rod side chamber,said second fluid distribution means, when in said first positionprovides fluid to said rod side chamber at a pressure lower than 20 bar.6. The device as claimed in claim 1 wherein said second fluiddistribution means includes a third position in which the distributionof fluid is reversed relative to said first position corresponding toextending of said third point ram, actuation of said second fluiddistribution means to said third position being effected by an externalswitch.
 7. The device as claimed in claim 1 wherein said device forcontrolling includes an intermediate frame, said frame being U-shapedhaving a horizontal portion and opening downwardly in use and locatedbetween the ends of said two arms, and being connected thereto and saidimplement, said frame including two rams each connected at one end atspaced apart points to said horizontal portion of said frame and at theopposite ends at contiguous points on the tractor to define an anglebetween said rams, said angle having a vertex corresponding to saidthird point of attachment, said horizontal portion having a centrallylocated attachment for the implement.
 8. The device as claimed in claim7 wherein said two rams of said frame each include a piston having a ramside and said second distribution means includes a fluid path in saidfirst position forming a bridge placing said ram sides of said rams incommunication with one another with the sides opposite said ram sidesbeing connected to a tank.
 9. The device as claimed in claim 8 wherein athird distribution means is provided having first and second positionsand connected by a fluid line in parallel to a line connecting saidsides opposite said ram sides, said third distribution means, in saidfirst position thereof, linking said sides opposite said ram sides to alow pressure reservoir and, in said second position thereof, linkingsaid sides opposite said ram sides to a source of fluid undersubstantially the same pressure as the ram side of said two rams sothat, extension of the rams will be effected to assist attachment of athird point of said implement after connection of said two arms to saidimplement.
 10. The device as claimed in claim 7 wherein saidintermediate frame includes along said horizontal portion two rearwardlyprojecting flanges each having a hole for attaching an adjustable lengththird point bar.
 11. The device as claimed in claim 10 wherein saidthird point bar is provided with an automatic hook for coupling by auser located remotely from said third point bar, indicating means beingprovided for indicating the locking condition of said hook.
 12. Thedevice as claimed in claim 1 wherein said attachment means for said twoarms allows relative motion of said two arms with respect to one anotherincluding different inclinations.